1. Field of the Invention:
This invention relates to an electronic endoscope apparatus wherein the patient circuit side and secondary circuit side are insulated from each other.
2. Related Art Statement:
Recently, there is extensively utilized an endoscope whereby organs within a body cavity can be observed by inserting an elongate insertable part into the body cavity or various curing treatments can be made as required by using a treating tool inserted through a treating tool channel.
There are also suggested various electronic endoscopes of a system wherein such solid state imaging device as a charge coupled device (CCD) is provided as an imaging means in the tip part of an insertable part so that a picture image information may be taken out as a photoelectrically converted electric signal.
Now, in the case of a medical electronic endoscope, a circuit part (patient circuit) inserted into the body of a patient and a circuit part (secondary circuit) connected to such peripheral device as a monitor must be isolated from each other.
FIG. 14 shows an example of the formation of such electronic endoscope apparatus.
In this drawing, the image of an object to be imaged is formed on a solid state imaging device 3 by an image forming optical system 2 and the signal photoelectronically converted by this solid state imaging device 3 is fed to a video signal processing circuit 5 through a cable 4. As this video signal processing circuit 5 is connected to such peripheral device as a monitor, the video signal must be isolated on the patient circuit side and secondary circuit side by an isolation circuit 6 within the video signal processing circuit 5.
There is such isolation system as a system wherein the output of the solid state imaging device 3 is passed directly through an isolation transformer or a system wherein, for example, in the case of a CCD, a signal taking the difference between a signal delaying the original signal by half the pixel sampling period and the original signal is passed through an isolation transformer to sample the effective signal part.
As such a Prior Art example mentioned above, one is disclosed in a Japanese utility model application Laid Open No. 198161/1982.
However, in the case of isolating the patient circuit and secondary circuit from each other, the output of the solid state imaging device has a low frequency component in the signal and therefore can not be directly passed through the isolation transformer. Also, in the case of the CCD output, the signal taking the delay difference can be passed through the isolation transformer. However, there is a problem that, when the signal is passed through the transformer, the high frequency component of the signal will attenuate and therefore no positive sampling will be able to be made.
Here, measures of reducing the noises of the solid state imaging device may be positively taken on the patient circuit side. In this case, there is a defect that, as the signal band is only a base band, the signal can not be transmitted with the isolation transformer.